Many internal combustion engines, whether compression ignition or spark ignition engines, are provided with fuel injection systems to satisfy the need for precise and reliable fuel delivery into the combustion chamber of the engine. Such precision and reliability is necessary to address the goals of increasing fuel efficiency, maximizing power output, and controlling the undesirable by-products of combustion.
A fuel injector is a precision device that must meter the quantity of fuel required for each cycle of the engine and must develop the high pressure necessary to inject the fuel into the combustion chamber at the correct instant of the operating cycle. Many fuel injectors utilize a mechanical linkage from the engine, such as a push rod and rocker arm, to pressurize the fuel charge and obtain the desired fuel spray pattern. It is desirable to maintain a lubrication coating between the engaging surfaces in the mechanical linkage to reduce wear, spalling and metal fatigue. A top stop facilitates lash between the parts to enable proper lubrication therebetween. The mechanical linkage interacts with a plunger that is disposed within a bore formed in the fuel injector for engaging a fuel. This mechanical pressurization of the liquid fuel produces an extremely high fuel injection pressure, often exceeding 20,000 p.s.i.
In the past, designers of internal combustion engines have generally used a mechanical clamping device to hold a fuel injector on the cylinder head. One approach is to affix a clamping device having a wishbone shaped fork at one end to the cylinder head. The clamping device is bolted to the cylinder head and the forks on the wishbone shaped end contact the top surface of the fuel injector body in two places, thereby holding the fuel injector in place. A second approach is to utilize a clamping plate that engages a flange formed on the outer perimeter of the fuel injector body. The clamping plate is secured to the engine by one, or a pair of bolts, thereby drawing the flange towards the engine block and holding the fuel injector in place.
These two approaches of fastening a fuel injector to an internal combustion engine have a common limitation. The common limitation being that the mechanical clamping device imparts a concentrated clamping force to a portion of the fuel injector body. The concentrated clamping force distorts the bore formed in the fuel injector body thereby causing plunger scuffing, and ultimately the seizure of the plunger within the bore. Premature failure of the unit fuel injector is often attributed to the fuel injector body receiving a concentrated clamping load.
In order to try and solve, or at least minimize, the foregoing problem, designers have tried different approaches. For example, there have been a variety of load distribution devices conceived of over the years, for transferring static clamping loads produced by clamping devices. For example, U.S. Pat. No. 5,566,658 to Edwards et al. discloses a fuel injector top stop and load distributor for reducing the clamp load transmitted to an injector barrel from a fork clamp. The load distributor housing includes a pair of openings for receiving respective legs of the fork clamp. A top cap is threadedly attached to the load distributor housing to form a top stop for limiting the outward movement of the plunger assembly. The barrel includes a thin walled tower or cylindrical extension which functions to guide the plunger assembly. The thin walled extension also enables the top stop and load distributor housing to be securely fastened to the barrel using, for example, a groove and snap ring arrangement. The load distributor housing includes an annular ring formed on its lower surface for advantageously transferring the clamping load radially inward towards the center of neutral axis of the fuel injector body thereby resulting in a decrease in the distortion of the plunger bore in the thin walled barrel extension. However, Applicant has determined that the thin walled barrel extension is very sensitive to the clamping load and still experiences an unacceptable degree of distortion resulting in poor performance and reliability. Moreover, the top stop and load distributor must be precisely located relative to the barrel to minimize distortion thereby complicating the assembly process and increasing costs. In addition, the thin walled section of the barrel is difficult and, therefore, costly to manufacture. Likewise, the openings in the top stop and load distributor housing result in unnecessary manufacturing time and expense. In addition, the use of separate top stop components, i.e. a top stop cap and lock nut, which thread onto the load distributor housing, undesirably increases the complexity and cost of the assembly.
U.S. Pat. No. 4,601,086 to Gerlach discloses a top stop assembly, mounted on a fuel injector, which includes an annular collar having inner threads for engaging outer threads formed on the injector barrel, a top stop having outer threads for engaging the inner threads of the barrel and a locking nut for threadably engaging the outer threads of the top stop to position the top stop relative to the annular collar and the injector barrel. However, the use of separate top stop components undesirably increases the complexity and cost of the assembly. Also, the threaded connection between the annular collar and the barrel inherently necessarily creates lateral loads on the barrel possibly contributing to bore distortion.
Consequently, there is a need for a simple, inexpensive top stop assembly for a fuel injector which effectively distributes the clamping load to the injector barrel while minimizing injector bore distortion.